The present invention relates to a method and wrist-worn apparatus for monitoring states of consciousness, drowsiness, distress, and/or performance of a person, and particularly for the early detection of increasing drowsiness in a person in order to alert the person and possibly others in the near vicinity.
The state of increasing drowsiness is manifested by a number of physiological changes. The device implemented by this invention utilizes autonomic and/or central nervous system electro-physiological monitoring and/or automatic reaction time testing, for detecting the onset of drowsiness.
Recent 1998 statistics issued by the U.S. Department of Transportation revealed that drowsy drivers are the cause of some 60,000 accidents resulting in 45,000 injuries and 15,000 fatalities. This invention is thus particularly useful in safety and security applications. Examples of users in such applications include vehicle drivers, pilots, flight controllers, night shift workers and the military. The invention is thus applicable whenever drowsiness is to be detected to prevent accidents and particularly distinguishes from traditional methods that analyze brain waves, eye movements, steering wheel movements and other means described in the published literature.
This invention may also be used as an adjunct to monitoring in a sleep laboratory or at home, to in depth anesthesia monitoring, and to various diagnostic monitoring, particularly when a memory module is attached.
An object of the present invention is to provide an improved method and apparatus for the physiological monitoring and alerting for events indicating increasing drowsiness, which method and apparatus do not require any sensors or electrodes (IR, EEG, EOG, etc.) to be affixed to a person""s head, which makes the apparatus and method particularly useful in the above mentioned applications, as well as in a wide variety of other applications.
According to one aspect of the present invention, there is provided apparatus for detecting the onset of drowsiness in a person while gripping an object, particularly a vehicle driver gripping a vehicle steering wheel, comprising a wrist band to be worn by the person; an electrical sensor to be pressed by the wrist band, when worn by the person, into contact with the skin of the person for sensing a physiological condition thereat and for outputting electrical signals corresponding thereto; and a processor for processing the electrical signals and for producing an indication therefrom of the onset of drowsiness in the person.
According to further features in the preferred embodiments of the invention described below, the processor produces from the electrical signals a measurement of changes in muscular activity at the person""s wrist, and utilizes such measurements in producing an indication of the onset of drowsiness in the person.
Several embodiments which are described below wherein the electrical sensor includes a plurality of electrodes for detecting electromyographic (EMG) electrical impulses produced by the person""s wrist muscles which are processed by the processor for producing said measurements of muscular activity utilized in producing the indication of the onset of drowsiness.
According to further features in the described preferred embodiments, the electrical sensor further includes a thermistor for detecting changes in the skin temperature, which changes are also utilized in producing said indication of the onset of drowsiness in the person.
According to still further features in the described preferred embodiment, the electrical sensor also includes a vibro-tactile stimulator, and the processor also measures the reaction time from actuation of the stimulator to the response in the physiological condition, and utilizes the reaction time for producing an indication of the onset of drowsiness in the person.
According to another aspect of the present invention, there is provided an electrical sensor mountable in a shock-absorbing manner to an object for sensing a condition therein, particularly to the wrist of a person for sensing the onset of drowsiness, comprising: a first cup-shaped member of circular configuration including an annular rim extending outwardly from one side of the member for engaging with the object, a center region within the annular region, and an annular yieldable juncture joining said annular rim with the center region; a detector fixed to the center region within the rim and extending outwardly of the rim on one side of the cup-shaped member; and a band applied over the opposite side of the cup-shaped member to apply a force pressing the rim firmly against the object when mounted thereon, and also pressing, via the annular yieldable juncture, the detector firmly against the object.
According to still further aspect of the present invention, there is provided a method for detecting the onset of drowsiness in a person while gripping an object, particularly a vehicle driver while gripping a vehicle steering wheel, comprising: pressing an electrical sensor into contact with the skin of the person""s wrist for sensing a physiological condition thereat and for outputting electrical signals corresponding thereto; and processing the electrical signals for producing an indication therefrom of the onset of drowsiness in the person.
A major advantage of the present invention is the absence of head-mounted electrodes and sensors. Particularly, brain waves and eye movements are traditionally measured with electrodes that require gels or pastes to be applied for making a good electrical contact, and further require mechanical or adhesive means for holding such electrodes in place. The minute EEG signals are prone to interfering signals arising from wire movements. Moreover, the application of the electrodes and lead wires to the scalp results in an unsightly appearance. In addition, EEG brainwaves signals are generally contaminated by EOG eye movement signals that act as interfering signals which have to be removed by special algorithms requiring substantial computer power before further EEG analysis of the brainwaves can be made.
The present invention, however, enables the monitoring device to be self-contained and to have no wires thereby enabling more conventional use and cleaner signals in hostile environments of radio frequency interference.
The parameters monitored are analog signals in nature. In the described preferred embodiments, they are amplified, filtered, and converted into a digital format for further processing by an embedded single chip computer. For each parameter an individualized baseline is computed and stored in a RAM memory. A trending is performed on each parameter. When the trended value divided by the baseline deviates from a preset percentage value stored in memory, a parameter alert flag is raised.
To transmit an overall alert flag, the device makes a decision based on majority of parameter alert flags being raised, on any single alert flag, or any desired combination of alert flags.
The first parameter alert flag identifies the violation of peripheral pulse rate variability preset. The pulse is sensed, amplified, filtered, converted from analog to digital and analyzed by the computer for beat-to-beat validity following software dicrotic notch detection. Extraneous pulses are rejected by the algorithm. The pulse rate variability is performed by spectral analysis of the beat-to-beat period. Increasing drowsiness is accompanied by decreasing pulse rate and variability thereof.
The second parameter alert flag identifies the violation of peripheral vasomotor response preset. The high-resolution skin temperature is sensed by a miniature bead thermistor, then amplified, filtered, converted from analog to digital and analyzed by the computer for peak-to-peak amplitude. Extraneous waveforms are rejected by the algorithm. Increasing drowsiness is accompanied by decreasing vasomotor tone variability due to the power sympathetic mediation.
The third parameter alert flag identifies the violation of muscle tone preset. The forearm EMG is detected by the wrist electrodes. The EMG signal is amplified, filtered, converted from analog to digital and analyzed by the computer following software rectification and integration for peak and average amplitudes. Increasing drowsiness is accompanied by decreasing muscle tone and muscle tone variability thereof.
The fourth parameter alert flag identifies the violation of peripheral blood flow presets. The limb""s blood flow is sensed from the electrical impedance of the wrist band electrodes. The signal is amplified, filtered, detected, rectified and converted from analog to digital and levels are analyzed by the computer. Increasing drowsiness is accompanied by decreasing blood flow due to decreasing systolic blood pressure.
The fifth parameter alert flag identifies the violation of reaction time. Vibrotactile stimulation is automatically and periodically performed by a miniature concentric motor or any other suitable device. The above mentioned electrodes sense the skin potential response between any two points on the wrist. The skin potential response signal is amplified, filtered, polarity detected, and converted from analog to digital, and levels, polarity and delay following vibrotactile excitation are analyzed by the computer. Increasing drowsiness is accompanied by increasing reaction time as well as increasing tactile sensory and autonomic arousal thresholds.
The above mentioned electrodes and sensors are preferably dry (pasteless). Special means are provided by the present invention to assure shock absorption capabilities to sensors and electrodes, in order to enable reliable detection of minute signals with minimal mechanically-induced movement artifacts. Each shock absorber mechanically isolates a sensor or electrode with two independent suspensions, placing a constant pressure on the sensor or electrode which varies as a only one part in several hundreds as result of wrist movement and varying accelerations. The first order mechanical buffering is provided by a spring that suspends each sensor or electrode in an inverted cup that buffers the sensor or electrode from the surrounding skin. The second order mechanical buffering is provided by an air-cuff that closes around the wrist with Velcro type closure that further suspends the inverted cups.
A wireless communication link is preferably provided to a further remote apparatus that provides an audio-visual alert signal for the detection of increasing drowsiness. The remote apparatus may contain a clock and provide an optional periodic xe2x80x9crestxe2x80x9d audio-visual reminder signals during the xe2x80x9credxe2x80x9d hours when drowsiness may be at its peak. It further serves as a logger or recorder with PC download capability to record and identify the various flags by coding each one uniquely.